Manufacture of sponge rubber articles



Patented Apr. 14, 1925.

UNITED STATES PATENT OFFICE.

FRANK S. MALM, OF CHICAGO, ILLINOIS, ASSIGNOR TO WESTERN ELECTRIC -('JOllilIIE'AINY.

INCORPORATED,

0']? NEW YORK, N. Y., A CORPORATION OF NEW YORK.

MANUFACTURE OF SPONGE RUBBER ARTICLES.

' Application filed February 28, 1923. Serial- No. 621,751.

To all whom it may concern:

Be it known that I, FRANK S. MALM, citizen of the United States, residin Chicago, of Illlnois, have inventedcertain new and useful Improvements in the Manufacture of Sponge Rubber Articles, of which the following is a full, concise, clear, and exact description. This application is a continuaa at tion in part ofm'y co-pending application,

articles,

- the human sk Serial No. 279,171, Patent No. 1,484,731, filed February 25, 1919.

This invention relates to sponge rubber and more particularly to ear pieces for aviators telephone head sets and the manufacture thereof.

The invention has for its object the protection of sponge rubber articles from deterioration by oxidation and to better adalpt such articles when used in aviators te e phone head sets or the like for contact with In accordance with the general features of this invention the sponge rubber articles are provided with an outer coating of smooth surfaced rubber which is applied thereto in the process of the manufacture of the articles.

In the preferred form of the invention the coating for the articles is.applied in the molding or forming and vulcanizing' steps by which the body 1s roduced.

This may be accomp ished by covering the interior surface of the mold with a coating of rubber compound which will, on formation and vulcanization of the sponge rubber body, become attached thereto to form the coating surface of the article.

In the drawingslin which this invention is illustrated in connection with a receiver ear iece for aviators head sets F1g. -1 is a cross-sectional view of the completed article;

Fig. 2 is a cross-sectional view ofrthe mold showmg parts in place prior to the forming and vulcanizationprocesses, and Fig. 3 is a plan view and one section of the mold indicatin the form'of the article.

In the ractice o the processes ofthis invention' t e body portion of the article is formed of a rubber composition containing in the county of Cook and tate substantially the following ingredients in the proportions given Per cent.

Smoked sheet rubber, ap-

proximately 37.000

Coucho rubber 28.375

Ammonium carbonate 17. 625

Vermillion English pale 4. 250

While this composition may be varied both as to the ingredients and amounts, the one glven has been found to produce an article which satisfactorily meets special requirements for articles of this kind.

The M. R. substitute may be any suitable asphaltic compound. The accelerator may be either organic or inorganic, such as magnesium oxide or basic amino compound.

The Coucho rubber is included in this compound to facilitate the workability of the mixture; the sulphur forthe vulcanizing agent; the barytes is a. filler which in the colored articles is used to control the shades; the paraffin and M. R. substitute facilitate the mixing of the compound and also retard oxidation of the finished product, and

ammonium carbonate is used to obtain the gas generated to produce the cellular structure of the compound.

It will usually be found preferable to addthe ammonium carbonate to the batch just prior to its use, and in order to facilitate -the blowing of the batch a suitable volatile rubbersolvent, preferably benzol, is added with the ammonium carbonate; The benzol or other volatile rubber solvent renders the batch more plastic, so that i the volatile ingredients of. the rubber solvent and ammonium carbonate can more easily force the soft compound into all cavities of the mold, thereby facilitating the formation of a erfectly molded art. Itis found prefera 1 with a batch includin ingredients in the proportions above notec l to include approximately ten er cent of the-benzol or other volatile rub r solvent.

The composition of the. above description is thoroughly mixed, and the blank 5 formed therefrom is placed between upper and lower mold members6 and 7.

Prior to the placin of this blank 5 in the molds, however, t e inner surfaces of .the mold members 6 and 7 have been treatmetal mold. With the several elements in benzol gases.

the mold the two members 6 and 7 are clamped together and the loaded molds are put into a vulcanizer, to which compressed air is admitted, and the vulcanizing period started and continued for approximately four hours at an'air pressure of 55 pounds per square inch, the steam pressure in the acket being maintained atapproximatel 110 pounds pressure per square inch.

During the early riod in the vulcanizer the ammonium car nate decomposes and is broken down into gases which escape from the compound in the molds which are vent-ed, as indicated-at 10 and 11, and cause...

the cellular structure of the rubber which gives to it its spongy characteristics.

The air pressure in thiscase retards the too rapid escape of'gases which are to cause sponging, prevents entire volatilization of the solvent, and serves also to retard the compound which is plastic at this temperature from escaping through the vents 10 and 11 in the molds. This pressure, however, does not prevent the u timate escape of the ammonium carbonate gases or of the The coating or layer 8 of the rubber compound to whlch the interior of the mold is treated the blank 5, and the ring 9 being in a plastic condition, willbecome closely adherent as the blank 5 expands in response to the generation of the gases from the ammonium carbonate, and these several parts will, upon vulcanization, become securely fastened to produce the finished article 1n the form desired.

The smooth coated-surface of the article not only prevents the accumulation of foreign matter in the cellular structure, which -would be detrimental when used in contact with the human skin, but it also prevents the oxidation and deterioration of the rela-- tively-thin walls separating the cells of the structure, which would occur if these walls were exposed directl to the air.

Openings or notc 12 and 13 are provided in the mold members 6 and 7 for the insertion of tools for separating the molds after the several steps of the process have been completed.

What is claimed is: s

1. A process for the manufacture of a spongy rubber material, comprising mixing together rubber, a vulcanizing agent, a gas producing substance, a volatile rubber solvent, an acceleratorandthen vulcanizing said composition. 1

2. A process for the manufacture of a spongy rubber material, comprising mixing together rubber, a vulcanizing agent, a gas producing substance, a volatile rubber solvent, and magnesium oxide, and then vulcanizing said composition. j

3. A process for the manufacture of a spongy rubber material, comprising mixing together rubber, a vulcanizing agent,

a gas producing substance, an accelerator and benzol, and then vulcanizing said composition.

4, A process for the manufacture of a spongy rubber material, comprising mixing together smoked sheet rubber, sulphur,

ammonium carbonate, a filler, an accelerator and a volatile rubber solvent, and then -vulcanizing said material.

5. A process for the manufacture of a spongy rubber material, comprising mixing together smoked sheet rubber, sulphur, ammonium carbonatqea filler, am accelerator, and benzol, and then vulcanizing said material.

6. A process for the manufacture of a spongy rubber material, comprising mixing together smoked sheet rubber, ammonium carbonate, a. filler, magnesium oxide, and a volatile rubber solvent, and.

then vulcanizing said composition.

7. A process for the manufacture of spongy rubber material, comprising mixing together:

Per cent.

Rubber about 65 Ammonium carbonate 17 Filler 11% Sulphur 4 Magnesiumoxide 1 and then adding to the mixture benzol about 10%. I I

8. The herein described method of mak-' ing sponge rubber articles, consisting first in the formation of a composition of smoked 1.261;.

sheet rubber, a vulcanizing agent, a filler, a gas producing substance, an accelerator and a volatile rubber solvent, locating the composition within a mold, the composition sulphur, 7

but partially filling themol then'vulcanizing the composition in the mold, causing it to swell or expand andfill the moldand creating within the composition a large number of cells.

g sponge rubber articles, consisting first 9. The herein describedmethod of mak in the formation of a composition of smoked sheet rubber, sulphur, ammonium carbonate, a filler, and magnesium oxide in substantially the proportions stated, then locating said composition in a mold provided with openings for the escape of gases, partially filling the mold, and then vulcanizing-the composition in the mold. I

10. The herein described method of making sponge rubber articles, consisting first in the formation of a composition of smoked sheet rubber, sulphur, ammonium carbonate,

barytes or similar material, and an acoel erator such as tially' the proportions said composition in a.

openings for filling the mold, and composition in the mo In witness whereof, my name this M day magnesium oxide 1n substan- FRANK s. MALM.

stated, then locating.

of February A. D., 

